I think we need to contact Mark Harbin. He has had both CNBG and NBG in central Kansas for close to 20 years. I have both, problem is I am not "seeing" anything that is a visual que to ID offspring of the 2, only the RESxBG hybrids..
I know we stocked a freshly renovated impoundment NE of me even, with Harbin's CNBG over 3 years ago and they have exploded and done just fine reproduction-wise. In THAT impoundment, there are no NBG. When we stocked the Colby lake, my fish came out of the same load and I catch an occasional CNBG that is obviously from the original stocking as they are all the same, large size.
I will try and get some info from Mark.